As a mounting structure of an electronic component manufactured with a semiconductor element in a form of a package to be mounted onto a circuit board, there is a known structure in which protruding electrodes such as solder bumps are formed on the electronic component and connected to the circuit board. In any such mounting structure, it is necessary to reduce a magnitude of thermal stress during heat cycle testing in order to ensure reliability of bonding after mounting. In other words, it is essential to reduce thermal stress developed in bonded areas between the semiconductor element and the solder bumps caused by changes in a surrounding temperature after the mounting due to a difference in coefficient of thermal expansion between the semiconductor element and associated structure.